1. Field of the Invention
The present invention relates primarily to occupancy based load management systems for lighting, plug-load, and similar loads being managed to reduce energy use or to provide response to emergency and security inputs.
2. Description of the Related Art
Prior art occupancy based load management is based on onymous or named communication between an occupancy detection sensor and a zone controller. These two components determine if a zone is occupied and then modulate a connected electrical load accordingly. The basic operation of this communication was worked out over 20 years ago. A sensor detects motion, sound or another proxy for human presence and then communicates that status to a load controller that has traditionally been a relay.
Conventional Occupancy logic switches on the connected load when a zone becomes occupied and switches off that load when the zone becomes unoccupied. With more recent Vacancy logic the auto-off step is retained but the load is turned on manually. In actual operation, occupancy detection is often spotty so a delay timer is added to smooth out the process by creating a window of time during which the detected occupancy will reset the delay timer to keep the lights on.
The above process can also be described in terms of states. The zone starts in an unoccupied or idle state and changes to an occupied state when occupancy is detected. If the sensor is configured for occupancy logic there is an action associated with the state change to switch on the connected load. If vacancy logic is being used the load is assumed to be turned on manually. The occupied state continues until the occupied state timer times out. This timer is set to its timeout period each time that an occupancy proxy event is detected. If no proxy event is detected the timer times out and the auto-off process begins.
Multi-Sensor Operation—When zones are too large for a single sensor, multiple sensors are typically used to cover the space. The conventional solution has been to parallel wire multiple stand-alone sensors to a single load controller. When any one sensor detects presence and trips (changes from its idle to occupied state) it closes an internal switch which activates the controller. If the controller is a relay, the relay solenoid activates which then closes the relay and switches on the connected load. As more sensors detect occupancy, they also trip but no additional action occurs because the zone is already in the occupied state. However, as the zone becomes unoccupied all the parallel wired sensors must return to their idle state before the zone becomes fully unoccupied and the electrical load is allowed to turn off. In Boolean logic terms the on function is an OR gate and the off function is an AND gate.
The parallel wired approach has worked well but is cumbersome and restrictive. Parallel wired sensors require long cable runs and 3-wire polarized connections that can be miss-wired. They also have limited capacity due to available power of the controller. Power limits can be addressed by power boosters but in larger rooms and corridors there is little that can be done about long cable runs. Additionally, adding additional sensors or making other changes to the zone operation require rewiring and each sensor adjustment must be made manually at each sensor. In small applications these limitations are likely not significant but in larger buildings the act of individually maintaining hundreds and even thousands of sensors can be overwhelming.
Networking sensors together has the potential to addresses these problems. However, as occupancy sensors have been adapted to networking, much of their operation has not changed. Prior art networked sensors continue to operate as independent devices and act as if they were parallel wired. In order to make this work the zone controller must know how many sensors are covering a zone and must then keep track of the state of each sensor. This is done with an onymous communication from each sensor that is sent each time the sensor changes state.
To avoid these problems U.S. Pat. No. 8,009,042 B2 limits the number of sensors allowing the sensors and zone controller to be preconfigured. Zones with a variable number of sensors can be supported but only by offering products that are preconfigured for varying number of sensors or by providing some form of field configuration to set up the zone for a fixed number of sensors.
U.S. Pat. No. 8,009,042 B2 also acknowledges another problem with prior art networked sensors wherein the loss of any sensor in the occupied state will prevent the virtual circuit from clearing and returning to the unoccupied state. U.S. Pat. No. 8,009,042 B2 addresses this problem by adding a heartbeat function to detect any missing sensors but the fundamental problem caused by state-based logic remains.
Thus, what is needed is a new approach. Advanced lighting control systems with sophisticated interactive occupancy detection, daylighting, and user control are becoming increasingly common due to their capacity to significantly reduce energy use and to deliver an enhanced work environment. However, as these systems become larger and more complex so too do the associated problems of installation, operation, maintenance, testing, and emergency operation. Networked systems have the potential to meet these new demands but the systems need to be flexible and adaptable enough to fully cover all spaces with minimal installation and be robust enough to detect problems and continue working even when sensors fail or are added, removed, or reconfigured.